This invention relates to metal medical components to be used inside the body.
Noninvasive medical procedures reduce the risk of surgery by introducing medical devices to a body cavity through small incisions or body orifices. The devices are carefully designed so that they may be controlled from the proximal end remaining outside the body to carry out the required treatment at the desired location inside the body. In one of the most common noninvasive techniques, angiography, a device, such as a guidewire, balloon angioplasty catheter or the like, is advanced and torqued at its proximal end to steer the device through a blood vessel to the position of an occlusion at which point a medical procedure such as balloon angioplasty and/or positioning of an endoprosthesis is carried out.
Typically, X-ray fluoroscopy is used to view the medical device within the body cavity to monitor placement and operation. The device may also be viewed by X-ray film after placement. To use these techniques, particularly with small devices which may be difficult to view, the medical device must include some radiopaque material, more dense than the surrounding tissue, to provide sufficient contrast on an X-ray image. A highly dense, and therefore particularly radiopaque, metal is usually incorporated with the portion of the medical device used inside the body for this purpose.
In interventional medicine, wires can be used for a variety of purposes such as tracking, stenting, filtering, conducting (electric current, ultrasound energy, etc.) and marking. Desirable attributes of these wires vary with application, but include properties such as stiffness, tensile strength, elasticity, radiopacity, weldability, flexural life, conductivity, etc. These properties are hard to find in single-material constructions. It is possible to achieve optimum properties by creating a multiple material coaxial construction. In medical wires, for example, it can be very desirable to have high radiopacity along with elasticity and strength. This may be accomplished by combining a radiopaque material with an elastic material. Although it is possible to put either material on the inside or outside, it would be preferable to put the dense radiopaque material (e.g., tantalum) on the inside (core) since dense materials are generally less elastic and the elastic material (e.g., titanium or nickel-titanium alloy) on the outside (clad). The clad or xe2x80x9cskinxe2x80x9d of the wire will undergo more deformation in bending than the core, so the elastic component is best positioned at the skin. In another medical application, it is desirable to have an elastic core (nitinol) for conducting axial vibrations (sonic or ultrasonic) and a thin stiff cladding (stainless steel) in order to minimize traverse vibrations which result in loss of energy.
An aspect of the invention is a metal medical device with at least a portion to be used within the body with properties that can be tailored to a particular application. The portion is formed of preferably two or more dissimilar metals joined together to form a unitary member. Typically, each metal contributes a desirable property to the device which is not substantially impaired by the presence of the other metal. In particularly preferred devices, one metal provides enhanced radiopacity. In these embodiments, the medical device comprises a metal outer member having a predetermined density and an exposed outer surface and a core including a metal having a density greater than the outer member to enhance radiopacity. The core is secured within and substantially enclosed by the outer member. Preferably, the medical component is in the form of a wire configured such that the mechanical properties, for example, the elastic properties, of the metal forming the outer member are affected by the core to a desired degree so that the wire has a desired overall performance suitable for its intended use. Preferably, the mechanical properties of the outer longitudinal member dominate the properties of the wire yet the radiopacity is substantially enhanced by the denser core. The invention also allows increased radiopacity of a metal medical device without adversely affecting and in some cases improving other important properties such as the biocompatibility, size or other performance characteristics. These performance advantages can be realized by proper selection of the material of the outer member and core, their relative size, and geometrical configuration. The performance characteristics of the component may be dictated by the medical device into which the radiopaque medical component is to be incorporated.
The term xe2x80x9cmetalxe2x80x9d as used herein includes electropositive chemical elements characterized by ductility, malleability, luster, and conductivity of heat and electricity, which can replace the hydrogen of an acid and forms bases with the hydroxyl radical and including mixtures including these elements and alloys. Many examples are given below.
In one aspect, the invention features a medical device having at least a portion for use within the body. The portion includes an extended metal outer member having an exposed outer surface and a core within the outer member formed of a metal different than the metal of the outer member. The core is secured within and substantially enclosed by the outer member.
Various preferred embodiments may include one or more of the following features. The extended metal outer member is comprised of a metal of predetermined density and the core is comprised of a metal having a density substantially greater than the outer member to enhance radiopacity of the device. The portion is in the form of a medical wire, wherein the metal outer member is a longitudinal member and the radiopaque core is positioned along the axis of the longitudinal member. The radiopaque core has a density of about 9.9 g/cc or greater. The core is selected from the group consisting of tungsten, tantalum, rhenium, iridium, silver, gold, bismuth, platinum and alloys thereof. The core has a modulus of elasticity of about 550 GPa or less. The core has a modulus of elasticity of about 200 GPa or less. The outer member is selected from the group consisting of superelastic alloys, precursor alloys of superelastic alloys, stainless steel, and titanium and its alloys.
The superelastical alloy is nitinol. The core is about 1 to 40% of the cross-sectional dimension of the component. The core is about 25% or more of the cross-sectional dimension of the component. The core is about 28% or less of the cross-sectional dimension of the component. The cross-sectional dimension of the component is less than about 0.025 inch. The outer member has a cross-section of about 0.0045 to 0.008 inch and the core member has a cross-section of about 0.0014 to 0.00195 inch inner diameter. The core is a solid metallic member. The outer member has portions of varying dimension. The outer member has a taper portion. The core has a constant inner dimension in portions corresponding to the varying outer dimension of the outer member. The portion is in the form of a medical guidewire. The portion is in the form of elastic leg members of a vascular filter. The outer member and core are of circular cross-sectional configuration. The portion is in the form of an ultrasonic probe. The probe is an elastic probe having a titanium core and nitinol outer member. The probe and core are constructed of materials of substantially different acoustic impedance. The acoustic energy is provided by axial excitation.
In another aspect, the invention features a medical wire device having at least a portion for use within the body. The portion includes an extended longitudinal metal outer member having a predetermined density and an exposed outer surface and a continuous solid core positioned along the axis of the outer member including a metal having a density of about 9.9 g/cc or greater and greater than the density of the outer member for enhancing radiopacity of the wire. The core is secured within and substantially enclosed by the outer member and is about 10 to 50% of the cross-sectional dimension of the portion for use within the body.
In various preferred embodiments, the core material is tantalum, the outer material is nitinol, and the cross-sectional dimension of the portion is about 0.025 inch or less. The outer member has a cross-section of about 0.0045 to 0.008 inch and the core member has a cross-section of about 0.0014 to 0.00195 inch inner diameter. The wire is in the form of a guidewire. The outer member has portions of varying dimension such as a taper portion. The core has a constant inner dimension in portions corresponding to the varying outer dimension of the outer member. The cross-sectional dimension of the portion is about 0.035 to 0.037 inch. The core is about 0.005 inch in diameter. The component is in the form of elastic leg members of a vascular filter.
In another aspect, the invention features a method for medical treatment by providing a medical device for performing a desired treatment, incorporating on at least a portion of the device a radiopaque medical component, formed of a metal outer member having a predetermined density and exposed outer surface and a core including a metal having a density substantially greater than the outer member to enhance radiopacity, the core being secured within and substantially enclosed by the outer member, and introducing the portion including the radiopaque medical component into the body, and observing the medical component by x-ray fluoroscopy.
In various preferred embodiments, the medical device is a guidewire and the medical component is a portion of the guidewire, the method further including steering the guidewire through the body from the proximal end. The medical device is a vascular filter.
In another aspect, the invention features a medical device capable of placement or manipulation in the body by means external of the body under guidance of a fluoroscope. The device is formed at least in part of an elongated wire-form metal member adapted to be subjected to elastic deformation to enable the device to be forced into a characteristic deformed configuration during a stage of use and to elastically self-recover from the deformation when deformation forces are relieved. The wire-form metal member is formed of a core of a first metal of a first selected thickness and an intimately surrounding sheath of a second selected metal of a second thickness, the first metal being a high density metal that demonstrates characteristic relatively high radiopacity and the second metal being a lower density metal having substantially more elasticity than the first metal, the combined effect of the selected thicknesses of the first and second metals in the wire-form member serving to enhance the radio-opacity of the wire-form member to provide improved fluoroscopic or x-ray visualization of the wire-form member in the body while imparting sufficient elasticity to enable the wire-form member to elastically self-recover from its characteristic deformed configuration.
In various preferred embodiments, the wire-form metal member comprises a draw-form. The second metal is nitinol. The high density metal is tantalum. The wire-form member comprises the main body of a medical guidewire.